The Right Reverend Michael Langrish, 66, is stepping down after 13 years as the Bishop of Exeter and his last service will be in June.
He had written in a local newspaper article: "Those who advocate 'same sex' or 'equal' marriage have sought to define opposition to this development as a 'faith' issue. That is simply untrue. It is a societal issue, as it redefines marriage and that will have consequences for us all."
He also said the common definition of marriage was of a union between a man and a woman, leading to consummation and potential for creating life.
He wrote: "Failure to consummate has been one of the grounds on which a marriage may be declared as invalid and annulled.
"What does consummation mean in the case of two people of the same gender?"
In a letter sent to all clergy in parishes across Devon, he said he had "grown to love this county and its people deeply".
He wrote: "During the 13 years that I have had the privilege of serving as Bishop of Exeter I have grown to love this county and its people deeply.
"Although 2012 has been a challenging year, as have many others before it, I hope that I leave the Church of England in Devon in good heart."